Image-guided surgery (hereinafter “IGS”) technology has been clinically available since the mid-1980's [1]. Analogous to a global positioning system (hereinafter “GPS”), IGS facilitates intra-operative surgical navigation by linking pre-operative radiographs to intra-operative anatomy. Central to the IGS process is registration—the linking of the radiographic images to the patient. To achieve high accuracy the registration is based on fiducial markers are identified in both the radiographs and on the patient. A mathematical transformation matrix is created to optimize the alignment of the fiducial markers. This same transformation matrix is then applied to all information in the radiograph allowing an overlay of the radiograph onto the patient's physical anatomy. This information is typically presented to the surgeon via a video monitor; a pointer placed within the surgical field is linked to a cursor on the monitor to show the corresponding radiographic position in axial, saggital, and coronal sections.
IGS is widely used in neurosurgery where the gold standard fiducial is a rigidly affixed N-frame. Screwed directly into the cranium, the N-frame is secured before imaging studies are obtained and remains in place throughout surgical intervention. Such stereotactic frames are invasive and cumbersome. However, given a life-threatening disease such as a malignant brain tumor, they are tolerated by patients. Neurosurgical studies have shown that IGS decreases operative time [2] and allows more complete resection of pathologic tissue while minimizing collateral damage [3].
As applied to otology and neurotology, IGS has found limited use. Isolated case reports describe their use in patients with unusual anatomy. Utilizing a modified neurosurgical unit, Sargent and Bucholz reported on IGS for middle cranial fossa approaches [4]. Raine et al. utilized an IGS system for split-electrode cochlear implant placement in a patient with cochlear ossification [5]. In perhaps the most widespread use, Caversaccio et al. reported their series of aural atresia repair using IGS guidance [6].
The reasons that IGS technology has found limited clinical application in otology/neurotology remain unclear. Hypothetically, its use has been stalled by the need for non-invasive, yet accurate, fiducial systems. To achieve submillimetric IGS accuracy—necessary to prevent damage to vital structures within the temporal bone—bone-affixed fiducial systems have been necessary. At present, less invasive fiducial systems are less accurate; skin-affixed markers achieve accuracies in the range of 1.5 mm and laser skin contouring achieves accuracies in the range of 2.5 mm [7, 8].
Therefore, a heretofore unaddressed need still exists in the art to address the aforementioned deficiencies and inadequacies.